The valence band structure in chalcopyrite Cu(In,Ga)Se2 films

The structure of the valence band at the Γ point of the Brillouin zone of Cu(In,Ga)Se₂ films is investigated on the basis of interference spectrophotometry data and an analysis of the structure of edge absorption within the framework of the quasicubic model of valence-band p-d hybridization in chalcopyrite compounds. The fundamental parameters of the quasicubic model associated with splitting of the valence band under the action of the tetragonal lattice field (Δ_cf), the spin-orbit interaction (Δ_so), and the degree of adulteration (hybridization) of the upper p-levels of the chalcogen by copper d states in Cu(In,Ga)Se₂ chalcopyrite films are determined. The dependence of the direct allowed transitions E _A , E _B , E _C on the composition of CuIn_xGa_1−x Se₂ solid solutions (for 0⩽x⩽1) is established. Fiz. Tekh. Poluprovodn. 31, 1033–1036 (September 1997)     

Heterojunctions utilizing CuInxGa1−xTe2 thin films

Polycrystalline CuIn_xGa_1−x Te₂ thin films are prepared by pulsed laser evaporation. The room-temperature hole densities and mobilities of the films are determined. It is established that direct optical contact of the postgrowth surface of such films with the surface of a cleaved InSe wafer exhibits the photovoltaic effect. The spectra of the relative quantum efficiency of photoconversion of the heterojunctions are investigated as a function of the composition of the CuIn_xGa_1−x Te₂ films and the photodetection geometry. It is concluded that the fabricated heterojunctions have potential applications in photodetectors of unpolarized radiation. Fiz. Tekh. Poluprovodn. 33, 824–827 (July 1999)     

Photosensitivity of thin-film structures based on laser-deposited CuIn(TexSe1−x )2 layers

Thin films of the solid solutions CuIn(Te_xSe_1−x )₂ (0<x<1) exhibiting chalcopyrite structure were obtained by the method of laser deposition. Using half-transmitting indium layers, Schottky diodes were prepared on the basis of the films obtained. The spectral dependence of the sensitivity as a function of the ratio between Te and Se was investigated by illuminating the structures through the In contact. Analysis of the experimental results showed that the region of spectral sensitivity of such thin-film structures depends on the tellurium content in the CuIn(Te_xSe_1−x )₂ layers. Fiz. Tekh. Poluprovodn. 32, 458–460 (April 1998)     

Electric and photoelectric properties of n-GaxIn1−x N/p-Si anisotypic heterojunctions

We have developed a technology for producing n-type Ga_xIn_1−x N/p-Si heterostructures by combined pyrolysis of indium and gallium monoammoniate chlorides, making it possible to obtain heterolayers with composition varying over wide limits (from GaN up to InN). The composition and basic electric and optical characteristics of nitride films were determined. The electric and photoelectric properties of the heterostructures with Ga_xIn_1−x N films of different composition were investigated. It was shown that the anisotypic heterojunction n-Ga_xIn_1−x N/p-Si is a promising photosensitive element for detecting visible-range radiation. The maximum values of the specific detectivity were D*=1.2×10¹¹ Hz^1/2·W⁻¹ at 290 K. A band diagram of the heterojunction was constructed. Fiz. Tekh. Poluprovodn. 32, 461–465 (April 1998)     

GaInAsSb/GaSb heterostructures grown in the spinodal decay region by liquid-phase epitaxy from Sb-enriched solution-melts

Nearly isoperiodic solitary Ga_1−x In_xAs_ySb_1−y /GaSb heterostructures, in which the composition of the solid solution should be found inside the region of spinodal decay (x⩽0.4), were grown by liquid-phase epitaxy from solution-melts enriched with antimony. On the basis of the results of a study of structural and luminescence properties of Ga_1−x In_xAs_ySb_1−y /GaSb heterostructures we have determined the main conditions ensuring reproducible growth of epitaxial layers, homogeneous in the composition of their solid solutions in the region where the existence of processes of spinodal and binodal decay have been theoretically predicted. It is shown that the magnitude and sign of the deformation which the layer undergoes during growth and also the thickness of the layer are the main factors influencing the properties of the growing GaInAsSb solid solutions in the spinodal-decay zone. Fiz. Tekh. Poluprovodn. 33, 1134–1136 (September 1999)     

Plasma-enhanced chemical vapor deposition and structural characterization of amorphous chalcogenide films

We describe the preparation of layers of amorphous Se, As_xS_1−x , As_xSe_1−x , Ge_xS_1−x , and Ge_xSe_1−x by plasma-enhanced chemical vapor deposition using the hydrides of the elements as precursor gases. We discuss the influence of the gas ratios and the deposition conditions (pressure, rf power input) on the chemical composition and the homogeneity of the binary systems. Information concerning the structure of the films was obtained from infrared and Raman spectroscopy. Fiz. Tekh. Poluprovodn. 32, 958–963 (August 1998) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Acceptors in Cd1−x MnxTe (x<0.1)

Acceptor defects, which control conductivity and recombination in Cd_1−x Mn_xTe (0⩽x⩽0.1), have been observed experimentally and investigated by electric and luminescence methods. The energy levels of the defects and the composition dependence of the energy levels have been determined. The physicochemical nature of these defects is discussed. Fiz. Tekh. Poluprovodn. 31, 1017–1020 (August 1997)     

Pressure-induced insulator-metal transition in electron-irradiated Pb1−x SnxSe (x⩽0.03) alloys

Galvanomagnetic effects (B⩽7 T) in electron-irradiated n-and p-type Pb_1−x Sn_xSe (x⩽0.03) alloys (T≈300 K, E=6 MeV, Φ⩽5.7×10¹⁷ cm⁻²) in the neighborhood of a pressure-induced insulator-metal transition (P⩽18 kbar) are discussed. The field dependences of the Hall coefficient calculated in terms of the two-band model are in satisfactory agreement with the experimental data, and the main parameters of the charge carriers in irradiated alloys are determined. It is shown that there is an increase in the hole concentration in the metallic phase under the action of pressure, associated with the motion of the energy bands at point L of the Brillouin zone, and that electrons overflow from the valence band into the band E _t1 of resonance states induced by electron irradiation; the parameters of this band are estimated. Fiz. Tekh. Poluprovodn. 32, 663–667 (June 1998)     

Long-wavelength photodiodes based on Ga1−x InxAsySb1−y wit composition near the miscibility boundary

The possibility of using liquid-phase epitaxy to obtain Ga_1−x In_xAs_ySb_1−y solid solutions isoperiodic with GaSb near the miscibility boundary is investigated. The effect of crystallographic orientation of the substrate on the composition of the solid solutions grown in this way is examined, and the indium concentration is observed to grow from 0.215 to 0.238 in the Ga_1−x In_xAs_ySb_1−y solid phase in the series of substrate orientations (100), (111)A, (111)B. A change in the composition of the solid solution leads to a shift of the long-wavelength edge of the spectral distribution of the photosensitivity. The use of a GaSb (111)B substrate made it possible, without lowering the epitaxy temperature, to increase the indium content in the solid phase to 23.8% and to create long-wavelength photodiodes with spectral photosensitivity threshold λ _th=2.55 μm. The primary characteristics of such photodiodes are described, along with aspects of their fabrication. The proposed fabrication technique shows potential for building optoelectronic devices (lasers, LED’s, photodiodes) based on Ga_1−x In_xAs_ySb_1−y solid solutions with red boundary as high as 2.7 μm. Fiz. Tekh. Poluprovodn. 33, 249–253 (February 1999)     

Solar cells based on CuIn1−x GaxSe2 films obtained by pulsed laser evaporation

Solar cells based on polycrystalline films of CuIn_1?x Ga_xSe₂ solid solutions were produced for the first time by the pulsed laser evaporation of source targets. The current-voltage characteristics of the cells were investigated, and the main photoelectrical parameters were ascertained. The optimal concentration of gallium ensuring maximal conversion efficiency of the thin-film solar cells and the films of the solid solutions with a chalcopyrite structure were determined.     

Distinctive features of the far-infrared reflection spectra of the semimagnetic semiconductors Hg1−x MnxTe1−y Sey

Reflection spectra of single crystals of Hg_1−x Mn_xTe_1−y Se_y (0.01<x<0.14, y=0.01) in the far-infrared range (10–600 cm⁻¹) are investigated at 300 and 77 K. A series of new phonon modes is observed, in addition to the longitudinal and transverse modes corresponding to the ternary compounds. Fiz. Tekh. Poluprovodn. 32, 546–548 (May 1998)     

Differential resistance of Au/GaAs1−x Sbx tunneling contacts in the zero-bias anomaly region. I. Contacts to n-GaAs1−x Sbx

The current-voltage characteristics and the differential resistance R(V)=dV/dI of Au/n-GaAs_1−x Sb_x tunneling contacts were investigated. Schottky barriers were prepared on n-GaAs_1−x Sb_x epitaxial layers, which were specially not doped, in the composition range 0.01<x<0.125. It was shown that the curves R(V) in the electron density range 2×10¹⁸⩽n⩽7×10¹⁸ cm⁻³ and temperature range 4.2⩽T⩽295 K are described well by the tunneling theory employing a self-consistent calculation of the potential in the Schottky barrier region. A square-root dependence of the conductance G(V)=(dV/dI)⁻¹ on the bias voltage V was observed in the zero-bias anomaly region in accordance with the Al’tshuler-Aronov theory of quantum corrections introduced in the density of states at the Fermi level by the characteristic features of the electron-electron interaction in disordered metals. Fiz. Tekh. Poluprovodn. 32, 574–578 (May 1998)     

Reactive Sputtering Process for CuIn1‐xGaxSe2 Thin Film Solar Cells

CuIn_1‐xGa_xSe₂ (CIGS) thin films are grown on Mo/soda lime glass using a reactive sputtering process in which a Se cracker is used to deliver reactive Se molecules. The Cu and (In_0.7Ga_0.3)₂Se₃ targets are simultaneously sputtered under the delivery of reactive Se. The effects of Se flux on film composition are investigated. The Cu/(In+Ga) composition ratio increases as the Se flux increases at a plasma power of less than 30 W for the Cu target. The (112) crystal orientation becomes dominant, and crystal grain size is larger with Se flux. The power conversion efficiency of a solar cell fabricated using an 800‐nm CIGS film is 8.5%.     

In0.2Ga0.8As/GaAs quantum well laser with C doped cladding and ohmic contact layers

Carbon doping in Al_xGa_1−xAs was achieved using different approaches. The moderate growth temperature of 650°C was employed to grow C bulk-doped Al_xGa_1−xAs with a high Al mole fraction. The hole-density was altered using different V/III ratios. The trimethylaluminum (TMAl) was used as an effective C δ-doping precursor for growth of C δ-doped pipi doping superlattices in Al_xGa_1−xAs. the average hole-density of C δ-doped pipi superlattices was greater than 2−3 × 10¹⁹ cm⁻³. Zn-free GRINSCH In_0.2Ga_0.8As/GaAs laser structures were then grown using the C bulk-doped Al_xGa_1−xAs and C δ-doped pipi superlattice as a cladding and ohmic contact layer, respectively. The ridge waveguide laser diodes were fabricated and characterized to verify flexibility of these two doping approaches for device structures.     

Study of Zn,Zn−Cd diffusion in In x Ga1−x As

 In this report,the diffusion of Zn,Zn-Cd in In_xGa_(1-x)As is investigated using ZnAs_2 and ZnAs_2+Cd as diffusion sources. The effect of the diffusion temperature,diffusion time,a variety of the diffusion source and composition x of the material on the relation of the(X_j-t~(1/2))are given.The diffusion velocity X_j~2/t of Zn in In_xGa_(1-x)As is faster than that of Zn-Cd in In_xGa_(1-x)As,and at 500-600℃,the surface acceptor concentration is from 1×10~(19)to 2×10~(20)cm~(-3),which is higher than that of Zn in InP.Reduction of contact resistance by use of In_xGa_(1-x)As contact layer for 1.3μm LED can be expected.     

Band-edge photoluminescence of heavily doped InxGa1−x As1−y Py(λ=1.2 µm)

Band-edge photoluminescence spectra of heavily donor-doped samples of In_xGa_1−x As_1−y P_y (x=0.77, y=0.53) were investigated in the temperature range (77–300) K. A theory of luminescence that takes into account fluctuations in the band-edge potentials due to nonuniform distribution of impurities is used to calculate temperature dependences of the positions and half-widths of peaks in these spectra. Good agreement is obtained between experimental and calculated curves. For heavily doped In_xGa_1−x As_1−y P_y samples with either p-or n-type conductivity, the peak energy of the band-edge PL is observed to shift towards lower frequencies at low temperatures. This shift is accompanied by broadening of the spectra and a decrease in the photoluminescence intensity compared to the analogous parameters for the spectra of undoped material. Possible mechanisms for radiative recombination are analyzed. Fiz. Tekh. Poluprovodn. 33, 907–912 (August 1999)     

Energy spectrum of n-type Pb1−x SnxTe (x=0.22) bombarded by neutrons

The effect of hydrostatic pressure (P⩽12 kbar) on the electrical properties of n-type Pb_1−x Sn_xTe (x=0.22) bombarded by electrons (T≈300 K, E=6 MeV, Φ=7.7×10¹⁷ cm⁻²) has been investigated. The restructuring of the energy spectrum of electronirradiated alloys under pressure has been investigated. The parameters of a model of the energy spectrum of charge carriers in electron-irradiated n-type Pb_1−x Sn_xTe (x=0.22) have been determined on the basis of the experimental data obtained. Fiz. Tekh. Poluprovodn. 31, 1021–1023 (August 1997)     

InGaAs/InP heterostructures with strained quantum wells and quantum dots (λ=1.5–1.9 µm)

Strongly strained In_xGa_1−x As/In_0.53Ga_0.47As/InP heterostructures with indium content x=0.69−1.0 in the active region were investigated experimentally and theoretically. Two types of structures were obtained by vapor-phase epitaxy from metalorganic compounds: 1) with isolated compression-strained quantum wells and 2) with self-organized nanosize InAs clusters (quantum dots). The temperature dependence of the quantum radiation efficiency of samples with quantum wells in the temperature range 77–265 K is characterized by T ₀=43 K. One reason for the low value of T ₀ is electron delocalization in the active region. The maximum radiation wavelength obtained in structures with quantum dots is 1.9 μm at 77 K. Fiz. Tekh. Poluprovodn. 33, 1105–1107 (September 1999)     

Acceptor and donor doping of AlxGa1−xN thin film alloys grown on 6H-SiC(0001) substrates via metalorganic vapor phase epitaxy

Thin films of Si-doped Al_xGa_1−xN (0.03≤x≤0.58) having smooth surfaces and strong near-band edge cathodoluminescence were deposited at 0.35–0.5 μm/h on on-axis 6H-SiC(0001) substrates at 1100°C using a 0.1 μm AlN buffer layer for electrical isolation. Alloy films having the compositions of Al_0.08Ga_0.92N and Al_0.48Ga_0.52N exhibited mobilities of 110 and 14 cm²/V·s at carrier concentrations of 9.6×10¹⁸ and 5.0×10¹⁷ cm⁻³, respectively. This marked change was due primarily to charge scattering as a result of the increasing Al concentration in these random alloys. Comparably doped GaN films grown under similar conditions had mobilities between 170 and ∼350 cm²/V·s. Acceptor doping of Al_xGa_1−xN for x≤0.13 was achieved for films deposited at 1100°C. No correlation between the O concentration and p-type electrical behavior was observed.